Method for producing carbon nanocomposite metal material and method for producing metal article molded therefrom

ABSTRACT

A method for producing a carbon nanocomposite metal material with increased carbon nanomaterial dispersibility and increased binding between carbon nanomaterial and matrix metal stock is disclosed. A preform obtained by mixing a matrix metal stock and microparticulate-coated carbon nanomaterial without the need for a dispersant and then compacting the material is maintained for a set time period at a temperature that is at or above the melting point of the matrix metal stock. In this state, the heat-treated body is reduced to a temperature that allows hot working, and a compacting treatment is performed.

FIELD OF THE INVENTION

The present invention relates to a composite metal material producedusing a carbon nanomaterial as a reinforcing material.

BACKGROUND OF THE INVENTION

The use of special carbon fibers referred to as carbon nanomaterials asreinforcing materials has received a great deal of attention in recentyears, and various activation methods have been offered. Carbonnanofiber (CNF) which is a typical example of a carbon nanomaterial is amaterial in which a sheet of carbon atoms arranged in a hexahedrallattice is wound in the form of a tube. The material is referred to as acarbon nanofiber (or carbon nanotube) because the diameter is 1.0 to 150nm (nanometers). The length is from a few micrometers to 100 μm.

When matrix metal stock is reinforced with carbon nanomaterial, it isnecessary for the carbon nanomaterial to be dispersed uniformly in thematrix metal stock. This type of dispersion technique is known, forexample, in Japanese Patent Application Laid-Open Publication No.2006-265686 (JP 2006-265686 A).

A method for producing a nickel (Ni)/carbon nanotube (CNT) compositesintered body using the dispersion technology disclosed in JP2006-265686 A referred to above is described in reference to the flowchart shown in FIG. 13 hereof.

In step (“ST” below) 101, the carbon nanotubes (CNTs), dispersant(sodium dodecyl sulfate), and solvent (purified water) are prepared, andthe materials are combined and stirred/mixed for 1 h using ultrasound(ST102). In addition, in ST103, nickel (Ni) powder, dispersant (ammoniumpolyacrylate), binder (polyvinyl alcohol), and solvent (purified water)are prepared, the materials are combined, and stirring/mixing is carriedout for 1 h using ultrasound (ST104).

The CNT suspension obtained in ST102 and the Ni slurry obtained in ST104are combined, stirred/mixed by ultrasonication (ST105), and then heatedto 80° C. and aggregated (ST106) to obtain an Ni/CT mixed slurry(ST107).

Next, the Ni/CNT mixed slurry is dried in two stages and compressed(ST108) to obtain a green molded body (ST109).

The resulting green molded body is defatted for 30 h (ST110) and then asintering treatment is carried out under compression in a vacuum(ST111). An Ni/CNT composite sintered body is thereby obtained (ST112).With this technology, a favorable CNT dispersion will be produced basedon inspection of the resulting Ni/CNT composite sintered body using amicroscope.

The following conclusions regarding the above conventional techniquewere confirmed by the inventors of the present invention.

Firstly, production costs are high due to the necessity of a defattingtreatment step (ST110) that lasts as long as 30 h.

Secondly, although dispersibility is favorable, the increase in strengthis not as great as expected.

Specifically, the conventional technology has room for improvement inregard to production costs and strength increase.

SUMMARY OF THE INVENTION

An object of the present invention is to offer a production technologywhereby strength can be improved while production costs can be reduced.

The inventors of the present invention conjectured that a lack ofadhesion between the CNF and matrix (Ni) is the reason that strength isnot improved as much as expected, in spite of the favorable dispersion.When adhesion is insufficient, slipping between the CNF and matrixoccurs when the composite deforms under external force, resulting in aloss of the CNF strengthening action.

Thus, investigations were carried out in light of the idea thatincreasing adhesion between CNF and the matrix is effective in additionto CNF dispersion. Sufficient results were thus obtained.

According to one aspect of the present invention, there is provided amethod for producing a carbon nanocomposite metal material, whichcomprises the steps of: preparing a matrix metal stock and amicroparticulate-coated carbon nanomaterial, obtained by bondingmicroparticles having an element that reacts with carbon to generate acompound, to the entire surface of a carbon nanomaterial; mixing themicroparticulate-coated carbon nanomaterial and the matrix metal stock;pre-molding by packing the resulting mixture; heating the resultingpreform to a temperature that is at or above the melting point of thematrix metal stock in a vacuum, inert gas, or non-oxidative gasatmosphere, and maintaining the heating temperature for a set timeperiod; compacting the resulting heat-treated body by performing coolingto a temperature that allows hot working of the matrix metal stock andperforming compression for a prescribed time period at this temperature;and cooling the resulting compacted body.

In this manner, according to the production method of the presentinvention, a microparticulate-coated carbon nanomaterial in whichmicroparticles containing an element that reacts with carbon to generatea compound are bonded to the entire surface of the carbon nanomaterialwas selected as the starting material.

For example, when a carbon nanomaterial is mixed directly with thematrix metal stock, the carbon nanomaterial coagulates and dispersionsuffers. In order to solve this problem, a dispersant has conventionallybeen added.

With the microparticulate-coated carbon nanomaterial used in the presentinvention, the surface microparticles exhibit a separating action, andthus a dispersant is not necessary. Because dispersant is not necessary,the defatting treatment step becomes unnecessary, allowing productioncosts to decrease.

When a preform produced by mixing and packing microparticulate-coatedcarbon nanomaterial and matrix metal stock is heated to a temperaturethat is at or above the melting point of the matrix metal stock and thenleft for a set time period, the melted microparticulate-coated carbonnanomaterial infuses into the matrix metal stock.

When, in this state, the temperature is reduced to a temperature atwhich hot-working is possible, and a compacting treatment is carriedout, the carbon nanomaterial and matrix metal are tightly bonded via themicroparticles, so the strength of the composite metal material can begreatly increased.

The temperature at which hot-working is possible is made as high aspossible. When this is done, compacting can be carried out with lowcompressive force, and there is no concern regarding constraints such asthe mold.

At temperatures that are lower than the temperature at which hot-workingis possible, undesirable effects such as poor workability and crackingoccur, and thus the compaction treatment is difficult. At hightemperatures that are above the temperature at which hot-working ispossible, a liquid phase state is produced, and leakage of the liquidphase occurs due to compression, so the compression force becomes lesseffective, making compaction difficult.

In the cooling step described above, it is preferred that the compactedbody described above be cooled during compression. At the time ofcooling, stresses will arise in the carbon nanocomposite metal materialdue to differences in the rate of cooling. In the present invention, thegeneration of stress is suppressed by compression. As a result, it ispossible to obtain a well-formed carbon nanocomposite metal material.

In the cooling step described above, an extrusion molding step iscarried out whereby the carbon nanocomposite metal material is extrudedand molded. Because the carbon nanocomposite metal material is extrusionmolded, the orientation of the carbon nanomaterial is increased, and acarbon nanocomposite metal material can be obtained that has superiormechanical strength, such as tensile strength.

It is preferred that the prepared microparticulate-coated carbonnanomaterial be produced by a mixed body formation step in which carbonnanomaterial and carbide-forming microparticles are mixed to obtain amixed body; and a vacuum vapor deposition step in which theaforementioned carbide-forming microparticles are evaporated under hightemperature and vacuum and are made to deposit on the surface of theaforementioned carbon nanomaterial. Consequently, the carbide-formingmicroparticles are uniformly bonded to the surface of the carbonnanomaterial, because the carbide-forming microparticles are evaporatedunder high temperature and vacuum and are bonded to the surface of thecarbon nanomaterial.

In the mixed body formation step, it is preferred that the organicsolvent, the carbide-forming microparticles, and the carbon nanomaterialbe introduced into the mixing container, stirred, and dried.Consequently, coagulation of the carbon nanomaterial can be prevented bythe organic solvent. The dispersed carbon nanomaterial can thus becoated with carbide-forming microparticles.

It is preferred that carbide-forming microparticles of Si or Ti be used.Both Si and Ti are metals that have a melting point that allows vacuumvapor deposition, and their wettability with respect to molten matrixmetal is also favorable. Si and Ti are both readily procured, and Si isparticularly inexpensive and thus desirable from the standpoint ofproliferation of the method of the present invention.

The matrix metal stock referred to above is preferably Mg or an Mgalloy. In the production method of the present invention, treatment iscarried out in a vacuum, and Mg and Mg alloy, which are susceptible tooxygen, can both be treated. Mg and Mg alloy are light metals, andbecause inclusion of carbon nanomaterial in these metals increasesmechanical strength, a structural material that is light and strong canbe provided which also has superior thermal transfer properties andabrasion resistance.

According to another aspect of the present invention, there is provideda method for producing a carbon nanocomposite molded article, whichcomprises the steps of: preparing a matrix metal stock and amicroparticulate-coated carbon nanomaterial, obtained by bondingmicroparticles having an element that reacts with carbon to generate acompound, to the entire surface of a carbon nanomaterial; mixing themicroparticulate-coated carbon nanomaterial and the matrix metal stock;pre-molding by packing the resulting mixture; heating the resultingpreform to a temperature that is at or above the melting point of thematrix metal stock in a vacuum, inert gas, or non-oxidative gasatmosphere, and maintaining the heating temperature for a set timeperiod; compacting the resulting heat-treated body by performing coolingto a temperature that allows hot working of the matrix metal stock andperforming compression for a prescribed time period at this temperature;cooling the resulting compacted body; and die-casting the carbonnanocomposite metal material obtained after the cooling step.

In the carbon nanocomposite metal material produced by the productionmethod for carbon nanocomposite metal materials, carbon nanomaterial isuniformly dispersed. By providing a material having this type ofuniformly mixed condition and carrying out die cast molding, molding ofmolded articles having complex shapes can be readily carried out, and acomposite metal molded article with high mechanical strength can beproduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain preferred embodiments of the present invention will be describedin detail below, by way of example only with reference to theaccompanying drawings, in which:

FIG. 1( a) to 1(d) are schematic views showing the mixed body formationstep and vacuum vapor deposition step of the present invention;

FIG. 2 is a schematic view showing the microparticulate-coated carbonnanomaterial;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2;

FIG. 4( a) to 4(c) are schematic views showing the preparation step, themixing step, and the preform step of the present invention;

FIG. 5 is a schematic view illustrating the treatment apparatus used inthe heating treatment step, compacting step, and cooling step of thepresent invention;

FIG. 6 is a graph illustrating the heating treatment step, compactingstep, and cooling step;

FIG. 7( a) to 7(c) are schematic views showing extrusion molding;

FIG. 8 is a schematic view showing die-cast molding;

FIG. 9 is an perspective view of a carbon nanocomposite metal moldedarticle produced by the cast molding apparatus shown in FIG. 8;

FIG. 10 is a graph shown a correlation between the added amount ofmicroparticulate-coated carbon nanomaterial and compression strength;

FIG. 11 is a graph showing a correlation between the added amount ofmicroparticulate-coated carbon nanomaterial and compression strengthsubsequent to extrusion molding;

FIG. 12 is a graph showing comparisons between Experiments 5 to 9 andExperiments 15 to 19; and

FIG. 13 is a flowchart showing the production steps for a conventionalcarbon nanocomposite metal material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1( a), an organic solvent (e.g., 1 L of ethanol) 11 isintroduced into a mixing container 10. Carbide-forming microparticles(e.g., 10 g of Si) 12 and a carbon nanomaterial (e.g., 10 g) 13 areintroduced into the organic solvent 11. Next, thorough stirring iscarried out with a stirrer 14 (e.g., 2 h at 750 rpm). Upon completion ofstirring, the material is suction filtered and dried thoroughly (e.g., 3h) in air at a high temperature (e.g., 100° C.), thereby producing amixed body 15 shown in FIG. 1( b). FIG. 1( a) and FIG. 1( b) togetherconstitute the mixed body formation step.

As shown in FIG. 1( c), the resulting mixed body 15 is introduced into azirconium container 16 which is covered with a zirconium lid 17. Thislid 17 is a non-sealing lid that allows passage of air between theinterior and exterior of the container 16.

As shown in FIG. 1( d), a vacuum furnace 20 is prepared having a sealedfurnace 21, a heating means 22 for heating the interior of the furnace21, stands 23, 23 for supporting the container 16, and a vacuum pump 24for evacuating the interior of the furnace 21. The container 16 isplaced in this vacuum furnace 20.

In the vacuum furnace 20, heating is carried out for 20 h at 1200° C. ina vacuum. By heating in a vacuum, the Si powder in the mixed body 15 isevaporated. The evaporated Si contacts the surface of the carbonnanomaterial forming compounds, and the material is bonded as Simicroparticles. FIGS. 1( c) and 1D constitute the vacuum vapordeposition step.

The structure of the resulting microparticulate-coated carbonnanomaterial is described in reference to FIG. 2 and FIG. 3.

With the microparticulate-coated carbon nanomaterial 30, the entiresurface of the carbon nanomaterial 13 is coated with a layer ofcarbide-forming microparticles 31 (microparticles containing an elementthat reacts with carbon to form a compound over the entire surface).

Because carbide-forming microparticles are bonded to the surface of thecarbon nanomaterial 13, an SiC reaction layer, for example, is formed atthe interface, and the carbide-forming microparticle layer 31 is tightlybonded to the carbon nanomaterial 13. Consequently, there is no concernregarding release of the carbide-forming microparticle layer 31 from thecarbon nanomaterial 13. In addition, the carbide-forming microparticlelayer 31 has additionally improved wettability with respect to thematrix metal relative to the carbon nanomaterial 13.

FIGS. 4( a), 4(b) and 4(c) show the preparation step, mixing step, andpreforming step.

In the preparation step of FIG. 4( a), the microparticulate-coatedcarbon nanomaterial 30 and a matrix metal stock 32 produced by cuttingfrom metal ingot are prepared.

In the mixing step of FIG. 4( b), the microparticulate-coated carbonnanomaterial 30 and the matrix metal stock 32 produced by cutting frommetal ingot are introduced into a container 33 and are thoroughly mixedwith a rod 34. The matrix metal stock 32 is, for example, pure Mg or Mgalloy.

In the preforming step of FIG. 4( c), a die 38 is placed on a base 37. Amixture 35 is then loaded into this die 38. Next, a punch 39 isinserted, thereby packing the mixture 35. The packed material is thepreform 41.

FIG. 5 shows the principle of the treatment apparatus used in theheating step, compacting step, and cooling step of this embodiment.

The treatment apparatus 50 is composed of a lower punch 51 that supportsthe preform 41, an upper punch 52 that is situated opposite the lowerpunch 51 and constricts the preform 41 or compresses (pressurizes) it ata compressive force P1, a heater 53 that surrounds the preform 41, achamber 54 that entirely surrounds the heater 53, preform 41, and thelike, an evacuation device 55 that is connected to this chamber 54 andplaces the interior of the chamber 54 in an evacuated state, and aninert gas suction device 56 that suctions argon inert gas into thechamber 54. This treatment apparatus 50 is controlled in accordance withthe control graph shown in FIG. 6.

FIG. 6 is a graph showing the heating step, compacting step, and coolingstep.

In the heating step, the interior of the chamber is placed in anevacuated condition, and an inert gas such as argon or a non-oxidativegas such as nitrogen is introduced while maintaining this evacuation orsubsequent thereto. Next, the preform is heated to 700° C. at aprescribed rate of heating (temperature elevation), and, upon reaching700° C., the material is maintained for 10 min to obtain a heat-treatedbody 57 shown in FIG. 5.

Because the melting point of Mg is 650° C., the matrix metal stock meltswhen heated to 700° C. and infuses into the microparticulate-bondedcarbon material. Thorough infusion is allowed to occur by retention for10 min.

By decreasing the setting temperature of the heater 53 shown in FIG. 5,the heat-treated body 57 is cooled to a temperature at which the matrixmetal stock can be hot-worked. Because the melting point of Mg is 650°C., if the material is cooled to 580° C. which is about 70° C.therebelow, the surface will thoroughly solidify, and there will be noconcern regarding leakage of the liquid phase under compression.

Upon reaching 580° C., the top punch 52 is lowered, and a pressure of 40MPa is applied to the heat-treated body 57. The material is maintainedfor 10 min at 580° C. under compression. During this retention, theupper punch 52 is gradually lowered. This lowering is continued for 5 to7 min, and subsequently lowering is stopped. When the upper punch 52 ismoving downwards, slight gaps are present in the structure, and the gapsare compacted. When the lowering of the upper punch 52 stops, it can beconcluded that sufficient density has been attained. The resultingcompacted body 58 is thus well compacted.

This compaction can be carried out at a temperature that allows hotworking of the matrix metal stock, but the required compressive forcefor compaction depends on the temperature. Compaction can be carried outwith a smaller compressive force when the temperature is high, andcompaction can be readily carried out even with carbon molds that arenot very strong. It is thus preferable to carry out compaction in atemperature range that is as high as possible.

Workability is poor at low temperatures that are below the hot workingtemperature, and with Mg or Mg alloy matrix metal stock in particular,cracking, fissures, and the like readily occur, making compactiondifficult.

At high temperatures in excess of the hot working temperature, aliquid-phase condition is produced, and leaking of liquid phase willoccur under compression, so the compressive force becomes lesseffective, making compaction difficult.

The resulting compacted body 58 can yield a carbon nanocomposite metalmaterial 59 when cooled to normal temperatures while being constrainedby the upper punch 52. In the compacted body 58, the surface temperaturedecreases first, and the temperature of the inner sections decreasesslowly. Thus, there are cases where stress referred to as cooling stressis generated due to the temperature differential. By continuedconstraint applied using the upper punch 52, it is possible to suppressthe generation of cooling stress. However, when there is no concernregarding cooling stress, cooling may be carried out without acompressive force (without the compacted body 58 being constrained bythe upper punch 52).

An example of extrusion molding of the unextruded carbon nanocompositemetal material 59 will be described below.

FIGS. 7( a), 7(b), and 7(c) are explanatory diagrams for the extrusionstep of this embodiment.

In FIG. 7( a), an extrusion apparatus 60 composed of a container 62having a hole 61 and a ram 63 is prepared, the container 62 is heated tothe prescribed temperature, and the carbon nanocomposite metal material59 is retained therein. Next, the ram 63 is extruded in the directionindicated by the white arrow.

In FIG. 7( b), an extruded carbon nanocomposite metal material 65 isobtained as a result of being extruded from the hole 61.

FIG. 7( c) shows the exterior of the extruded carbon nanocomposite metalmaterial 65, where carbon nanomaterial 13 oriented in the direction ofextrusion can be observed on a surface 66.

A sufficient amount of carbon nanomaterial 13 is contained on thesurface, thereby improving abrasion resistance.

Although not shown in the drawing, when a cross section of the carbonnanocomposite metal material 65 is observed, the carbon nanomaterial 13oriented in the extrusion direction can be observed in the crosssection. The carbon nanomaterial 13 is thus uniformly dispersed,increasing the mechanical strength.

FIG. 8 is a principle diagram for die-cast molding pertaining to thepresent invention, where a metal molding apparatus 70 is prepared forperforming die-cast molding. This metal molding apparatus 70, forexample, is preferably a die-casting machine apparatus wherein a plunger73 is housed in a heating tube 72 provided with a material feed port 71so that the plunger can undergo reciprocating movement. The plunger 73is driven by an injection cylinder 74, the main section is covered witha cover 75, and the end of the heating tube 72 meets a fixed plate 78. Afixed mold 79 is attached to the fixed plate 78, and by attaching amovable mold 82 to an opposing movable plate 81, a cavity 83 is formedbetween the molds 79 and 82.

The carbon nanocomposite metal material 65 shown in FIG. 7( c) or thecarbon nanocomposite metal material 59 shown in FIG. 5 is heated to apartially-melted temperature, thus producing a partially melted material84. This partially melted material 84 is then poured into the heatingtube 72 from the material supply opening 71 using the container 85 or asuitable supply mechanism. Next, by advancing the plunger 73, thepartially melted material 84 is injected into the cavity 83.

When heating is stopped at the partial melting temperature, the matrixmelt is a mixture of solid phase and liquid phase, and movement of thecarbon nanomaterial is restricted. As a result, dispersion of the carbonnanomaterial is maintained.

FIG. 9 shows that a carbon nanocomposite metal molded article 86 with acomplicated shape can be produced by the metal molding apparatus 70 ofFIG. 8.

The carbon nanocomposite metal material 65 produced by the method forproducing carbon nanocomposite metal materials has a uniformly dispersedcarbon nanomaterial. Because die-cast molding is carried out bysupplying material in this uniformly mixed condition, it is possible toreadily carry out molding, even with molded articles having complicatedshapes. In addition, a carbon nanocomposite metal molded article 86 canbe produced that has high thermal conductivity, mechanical strength, andabrasion resistance.

Experimental Examples

Experimental examples pertaining to the present invention are describedbelow, but the present invention is not restricted to these examples.

Mixed body formation step and vacuum vapor deposition step: As shown inFIG. 1, microparticulate-coated carbon nanomaterial was produced usingSi particles (carbide-forming particles) with a particle diameter of 4μm along with a carbon nanomaterial (gas phase-grown carbon fiber)having an average diameter of 150 nm and a length of 10 to 20 μm.

Preparation step: As shown in FIG. 4( a), the aforementionedmicroparticulate-coated carbon nanomaterial and Mg particles with apurity of 99.9% and a particle diameter 180 μm (or AZ91D, Mg alloyparticles) for use as matrix metal stock were prepared.

The composition of the Mg alloy as defined in ASTM AZ91D (magnesiumalloy die-cast JIS H 5303; product analogous to MDC1D) had an Al contentof about 9 wt %, with the remainder being trace elements, inevitableimpurities, and Mg.

Mixing step: As shown in FIG. 4( b), the microparticulate-coated carbonnanomaterial was mixed at 5 to 20 mass %.

Preforming step: As shown in FIG. 4( c), a preform was produced.

Heat treatment step: As shown in FIG. 5 and FIG. 6, 10-min retention wasperformed in an argon atmosphere at 700° C. (650° C. for AZ91D).

Compacting step: As shown in FIG. 5 and FIG. 6, 10-min retention wascarried out in an argon atmosphere at a compressive force of 40 MPa and580° C. (480° C. for AZ91D).

Cooling step: As shown in FIG. 5 and FIG. 6, cooling to normaltemperature was carried out while applying a compressive force of 40 MPain an argon atmosphere, thus producing a carbon nanocomposite metalmaterial with a diameter of 60 mm and a height of 20 mm.

First evaluation: Sample strips were cut from the carbon nanocompositemetal material prior to extrusion, and the compressive force wasmeasured. The measured values are presented in Table 1 below.

TABLE 1 (%: mass %) Micro- particulate- coated carbon Matrix metalCompression No. nanomaterial Pure Mg AZ91D strength Ratio Experiment 10% 100%  — 210 MPa (100  Experiment 2 10% 90% — 253 MPa 120 Experiment 315% 85% — 288 MPa 137 Experiment 4 20% 80% — 305 MPa 145 Experiment 5 0%— 100%  320 MPa (100) Experiment 6 10% — 90% 366 MPa 114 Experiment 715% — 85% 371 MPa 116 Experiment 8 20% — 80% 378 MPa 118 Experiment 930% — 70% 396 MPa 124

Experiments 1 to 4 employed pure Mg as matrix metal, and Experiments 5to 9 employed AZ91D as matrix metal. With Experiments 1 and 5, astructure was produced that contained no microparticulate-coated carbonnanomaterial for purposes of comparison. Experiment 4 gave a value of145, taking Experiment 1 as 100, and the compression strength increasedby 45% due to the 20 mass % content of microparticulate-coated carbonnanomaterial.

FIG. 10 is a diagram showing the correlation between the added amount ofmicroparticulate-coated carbon nanomaterial and the compressionstrength, where a graph was obtained by plotting the compressionstrengths of Table 1.

In Experiment 1 to Experiment 4, it was confirmed that compressionstrength increased in proportion to the added amount ofmicroparticulate-coated carbon nanomaterial. In Experiments 5 to 9 aswell, it was confirmed that compression strength increased in proportionto the added amount of microparticulate-coated carbon nanomaterial.

Next, an experiment was carried out in which an extrusion moldingprocess was carried out on the carbon nanocomposite metal material priorto the extrusion treatment.

Extrusion molding step: Extrusion molding was carried out in referenceto FIG. 7. Material was cut at a diameter of 43 mm and a height of 15 mmfrom the aforementioned carbon nanocomposite metal material and wasextruded under conditions of an extrusion temperature of 350° C., anextrusion ratio of 25, and a ram rate of 4 mm/sec, thus producing anextruded material with a diameter of 8 mm (extruded carbon nanocompositemetal material).

Second evaluation: A test strip (7 mm in diameter, 7 mm in height) wascut from the extruded material (extruded carbon nanocomposite metalmaterial), and the compression strength was measured. The measuredvalues are presented in Table 2 below.

TABLE 2 (%: mass %) Micro- particulate- coated carbon Matrix metalCompression No. nanomaterial Pure Mg AZ91D strength Ratio Experiment 110% 100%  — 299 MPa (100  Experiment 12 10% 90% — 350 MPa 117 Experiment13 15% 85% — 354 MPa 118 Experiment 14 20% 80% — 363 MPa 121 Experiment15 0% — 100%  412 MPa (100) Experiment 16 10% — 90% 432 MPa 105Experiment 17 15% — 85% 456 MPa 111 Experiment 18 20% — 80% 470 MPa 114Experiment 19 30% — 70% 475 MPa 115

For purposes of convenience, the test numbers were produced by adding 10to the number of Experiments 1 to 9, yielding Experiments 11 to 19.Specifically, extrusion was added to Experiment 1 in Experiment 11, andextrusion was added to Experiments 2 to 9 in Experiments 12 to 19.

Experiments 11 to 14 employed pure Mg as matrix metal, and Experiments15 to 19 employed AZ91D as matrix metal. With Experiments 11 and 15, astructure was produced that contained no microparticulate-coated carbonnanomaterial for purposes of comparison. Experiment 14 gave a value of121, taking Experiment 11 as 100, and the compression strength thusincreased by 21% due to the 20 mass % content of microparticulate-coatedcarbon nanomaterial.

FIG. 11 is a diagram showing the correlation between the added amount ofmicroparticulate-coated carbon nanomaterial and the compressionstrength, where a graph was obtained by plotting the compressionstrengths of Table 2. In Experiment 11 to Experiment 14, it wasconfirmed that the compression strength increased in proportion to theadded amount of microparticulate-coated carbon nanomaterial. InExperiments 15 to 19 as well, it was confirmed that the compressionstrength increased in proportion to the added amount ofmicroparticulate-coated carbon nanomaterial.

FIG. 12 is a graph that shows Experiments 5 to 9 and Experiments 15 to19 in parallel. In comparison to Experiments 5 to 9 in which extrusionmolding was not carried out, Experiments 15 to 19 that involvedextrusion molding showed an increased in compression strength of 90 to100 MPa. It was thus confirmed that the effects of extrusion molding aredramatic.

Although the details are not presented, a similar increase in mechanicalstrength was obtained when Ti was used instead of Si as thecarbide-forming metal (element that reacts with metallic carbon to formcompound). In addition to Si and Ti, zirconium (Zr) or vanadium (V) maybe used as the carbide-forming metal.

In addition to Mg or Mg alloy having a melting point of about 650° C.,Al or Al alloy having a melting point of about 660° C., Sn or Sn alloyhaving a melting point of about 232° C., or Pb or Pb alloy having amelting point of about 327° C. may be used as the matrix metal stock.

Obviously, various minor changes and modifications of the presentinvention are possible in light of the above teaching. It is thereforeto be understood that within the scope of the appended claims theinvention may be practiced otherwise than as specifically described.

1. A method for producing a carbon nanocomposite metal material,comprising the steps of: preparing a matrix metal stock of Mg or Mgalloy; preparing a microparticulate-coated carbon nanomaterial bybonding carbide-forming microparticles, which have an element thatreacts with carbon to generate a compound, to the entire surface of acarbon nanomaterial; mixing the microparticulate-coated carbonnanomaterial and the matrix metal stock; pre-molding by packing theresulting mixture to form a preform; heating the resulting preform to atemperature that is at or above the melting point of the matrix metalstock in a vacuum, inert gas, or non-oxidative gas atmosphere, andmaintaining the heating temperature for a set time period so as to causethe matrix metal stock to be completely melted and then to infuse intothe microparticulate-coated carbon nanomaterial; compacting theresulting heat-treated preform by performing cooling to a temperaturethat allows hot working of the matrix metal stock and that allows asurface layer of the heat-treated perform to thoroughly solidify toprevent the matrix metal stock in a liquid phase from leaking out fromthe heat-treated preform under compression, and performing compressionfor a prescribed time period at this temperature; and cooling theresulting compacted body.
 2. The method of claim 1, wherein the coolingstep comprises cooling the compacted body under compression.
 3. Themethod of claim 1, wherein the carbon nanocomposite material isextrusion molded after the cooling step.
 4. The method of claim 1,wherein the step of preparing a microparticulate-coated carbonnanomaterial comprises: a mixed-body forming step wherein a mixed bodyis obtained by mixing the carbon nanomaterial and the carbide-formingmicroparticles; and a vacuum vapor depositing step wherein the resultingmixture is introduced into a vacuum furnace, and the carbide-formingmicroparticles are evaporated in a high-temperature vacuum and bonded tothe surface of the carbon nanomaterial.
 5. The method of claim 4,wherein the mixed body formation step comprises introducing an organicsolvent, the carbide-forming microparticles, and the carbon nanomaterialinto a mixing container; and stirring and drying these contents.
 6. Themethod of claim 4, wherein the carbide-forming microparticles are Si orTi.
 7. A method for producing a carbon nanocomposite molded article,comprising the steps of: preparing a matrix metal stock of Mg or Mgalloy; preparing a microparticulate-coated carbon nanomaterial bybonding carbide-forming microparticles, which have an element thatreacts with carbon to generate a compound, to the entire surface of acarbon nanomaterial; mixing the microparticulate-coated carbonnanomaterial and the matrix metal stock; pre-molding by packing theresulting mixture to form a preform; heating the resulting preform to atemperature that is at or above the melting point of the matrix metalstock in a vacuum, inert gas, or non-oxidative gas atmosphere, andmaintaining the heating temperature for a set time period so as to causethe matrix metal stock to be completely melted and then to infuse intothe microparticulate-coated carbon nanomaterial; compacting theresulting heat-treated preform by performing cooling to a temperaturethat allows hot working of the matrix metal stock and that allows asurface layer of the heat-treated perform to thoroughly solidify toprevent the matrix metal stock in a liquid phase from leaking out fromthe heat-treated preform under compression, and performing compressionfor a prescribed time period at this temperature; cooling the resultingcompacted body; and die-casting the carbon nanocomposite metal materialobtained after the cooling step.
 8. The method of claim 7, wherein thecooling step comprises cooling the compacted body under compression. 9.The method of claim 7, wherein the die-casting step is carried out usingthe carbon nanocomposite metal material obtained by extrusion moldingthe carbon nanocomposite material obtained in the cooling step.
 10. Themethod of claim 7, wherein the step of preparing amicroparticulate-coated carbon nanomaterial comprises: a mixed-bodyforming step wherein a mixed body is obtained by mixing the carbonnanomaterial and the carbide-forming microparticles; and a vacuum vapordepositing step wherein the resulting mixture is introduced into avacuum furnace, and the carbide-forming microparticles are evaporated ina high-temperature vacuum and bonded to the surface of the carbonnanomaterial.
 11. The method of claim 10, wherein the mixed bodyformation step comprises introducing an organic solvent, thecarbide-forming microparticles, and the carbon nanomaterial into amixing container; and stirring and drying these contents.
 12. The methodof claim 10, wherein the carbide-forming microparticles are Si or Ti.